The present invention relates to methods and apparatus for detecting the presence of areas in the web where defects in moving paper webs, and in particular relates to a method and apparatus for detecting crepe wrinkles during paper re-reeling operations.
Defects in paper webs commonly occur during reeling operations. Such defects include crepe wrinkles, burst wrinkles and other weakened conditions in the web. The paper containing such wrinkles or other defects must be removed. Failure to remove the defective paper will likely cause web breaks during subsequent processing of the web.
At the end of a modern paper making machine, the paper is reeled at high speed onto a spool. It has been found that crepe wrinkles most commonly occur radially near the spool of the paper machine reel. From the paper machine, the paper reel is transported to a re-reeler. The re-reeler comprises an unwind station and a rewind station. When the web is re-reeled, crepe wrinkles that were near the spool of the original paper reel will be near the outer surface of the re-reeled reel. An operator may then remove or "slab off" paper containing crepe wrinkles and other defects. Paper may be slabbed off by manually cutting with a knife radially into the reel and across the reel. The slabbed off paper is unsuitable for sale.
A long standing problem in the industry i s accurately gauging how much paper should be slabbed off from the re-reeled reel. Because of high re-reeling speeds, the re-reeling crew often cannot accurately determine the location of crepe wrinkles or other defects. If the crew slabs off too little , defects will remain in the reel, which are likely to cause web breaks during later processing. If too much paper is slabbed off, it will result in a waste of saleable paper.
Various devices have been devised to detect wrinkles and other defects in moving paper webs. For example, U.S. Pat. No. 3,763,483 discloses an apparatus for mechanically "feeling" creases, bumps and other discontinuities in the surface of a moving web. U.S. Pat. Nos. 4,184,770 and 4,851,696 disclose devices that direct laser beams at or near the surface of a moving web. Variations in light received by a photoelectric sensor indi cate discontinuities, e.g., wrinkles, in the surface of the web. U.S. Pat. No. 4,160,913 scans the surface of the web with a small, rectangular "flying spot" light source. A detector receives reflected illumination. A hole in the web gives lower reflected illumination, while a wrinkle gives a higher than average illumination.
A draw back to the prior art devices is that each is designed to detect the presence of a wrinkle or defect itself. Since such defects are commonly very small, the surface area of the web relatively large, and the speed of the web fast, it exceedingly difficult to reliably detect defects. Invariably, the prior art detection equipment is either very sophisticated and expensive on the one hand, or unreliable on the other.
Accordingly, there is a long standing but unresolved need in the industry for a simple, inexpensive method and apparatus for reliably detecting crepe wrinkles and other associated defects and for accurately marking the location of the defective paper.